Preparation of seals between ceramic material and metal



- Patented oct. 1o, 1939 PATENT OFFICE PREPARATION OF SEALS BETWEENCERAM- IC MATERIAL AND METAL Thomas Robertson Scott and Leonard ArthurCharles Pooley, London, England, assignors to International Standard NewYork, N. Y. I Application January 7,

Electric Corporation,

1999, serial No. 249,826`

In Great Britain January 4, 1938 9 claims.

This invention relates to electrical ilttings such as sealing bells,potheads and the like which generally speaking comprise a porcelain orlike ceramic body fitted with a metal collar at each 5 end for mountingpurposes Aand/or for the connection of external electric circuitsthereto. In connection with such electrical fittings a diiiiculty arisesdue to the diierent thermal coeiiicient of expansion of the ceramic bodyand the l metal, and the invention is more particularly concerned withthe provision of sealing means between the ceramic part and. the metalpart of such electrical ilttings.

It is customary to attach the inetal parts of l the iittings to theporcelain body by means of -Portland cement, red lead or combinationsthereof which may be admixed with varnshes such as shel-lac to reducethe porosity of the material to oil or to clamp the porcelain body intothe metal with intervening gaskets but both of these methods are apt togive trouble due to the escape of insulating compound such as oil, with.which these electrical ttings are usuallyv lled which may lead toelectrical breakdown. Trouble may ina similar mannerbe caused by theingress of moisture or moisture laden air.

An object' of the invention is to overcome this diiliculty and with thisobject in view we provide, according to the invention, a method ofsealing the metallic part of an electrical fitting of the kind referredto (e. g. a pot-head) to the ceramic part thereof comprising providing alling of cementing'material consisting of styrene 'or an insulatingcomposition containing styrene between the metal and ceramic parts andthen obtaining the cementing effect between the parts by polymerisationoi the cementing materia-l in situ which expression includes advancingthe polymerisation of partially polymerised material. By means of thepolymerisation in situ the cementing material as it hardens bonds orwelds to the walls of the electrical fitting and thus affords aneiectiveseal.

The cementing material may comprise styrene plasticised according to U.S. patent application Ser. No. 190,032, filed February 11, 1938, whichteaches the method of plasticizing polymerized styrene by adding theretoan amount not over 25% of a chemically stable homocyclic carbon compoundhaving not less than two and not more than three fused rings, saidcompound having a boiling point higher than 240 C., and a symmetricalarrangement of polar groups, or styrene blended with rubber or the liketo which rubber plasticizers such as ceresin waxmay be added.

Alternatively, the cementing material may comprise styrene admixed withan aliphatic olene such as polyethylene or polyisobutylene to whichingredients such as rubber or materials according to our applicationSer. No. 190,032 may be added. The above cementing materials affordconsiderable resiliency at ordinary atmospheric lconditions andespecially if the polymerisation of the cementing material is controlledto give a product having a required degree of tenacity and resiliency.In this connection it may be mentioned that it is known that themechanical characteristics of polymerised styrene can be varied Withinwide limits, for example, by the selection oi the temperatures ofpolymerisation of the 15 material.

The cementing material is preferably applied y in a partiallypolymerised condition. 'I'his may be effected by stopping the`polymerisation process of the material at any desired point or bycompleting the polymerisation process and adding monomeric styrene tothe material prior to application thereof to the metal/porcelain jointor subsequently in situ prior to the polymerisation process. Thematerial is preferably bounded at the surface adjacent to the insulatingcompound, e. g. oil in the interior of the electrical tting by an oilresisting gasket seal. rFilis gasket may he constructed from astyrene/rubber blend so that during the polymerisation process thegasket is welded into the cementing material by the solvent action ofthe partially polymerised styrene on the styrene blend mentioned above.The main cementing material is also preferably bounded on the surfaceadjacent to the external atmosphere by seal which again should containstyrene to permit of it being Welded into the ceinenting material asdescribed above. 'I'his external seal should be of a material chosen forits Weather resisting characteristics. It may for example, consist ofstyrene/rubber which has been vulcanised. 1t should, however, beresilient. During the polymerisation process the cementing materialshould be maintained under external pressure so that polymerisationshrinkage, and also shrinkage during cooling down from thepolymerisation temperature is taken up by compression of the cementingmaterial. 'I'he compression of the gasket will also seal oil thecementing material from the atmosphere and prevent loss of monomericmaterial by volatllisation' during the polymerisation process.Preferably the cementing material is disposed between the wall of theceramic part and an upstanding iiange on the metal part of the iltting.

The cementing material may comprise monomeric or partially polymerisedstyrene loaded with paper, acetylated paper or other fibrous materialsuch as jute. A layer of Portland cement or like normal cement materialmay be superimposed at the surface exposed toethe atmosphere inrepairing end bells or the like.

In order that the invention may be clearly understood and readilycarried into effect reference is directed to the accompanying drawingwhich shows diagrammatically and by way of example a detail view of anelectrical fitting embodying the invention.

Referring to the drawing, l represents the ceramic e. g. porcelain partof the electrical fitting, 2 represents the metal part of the ttingwhich is provided with an upstanding flange 3 to retain the cementingmaterial indicated at 4. A compound resisting gasket 6 is shown on theinner surface ofthe cementing material 4 and a weather resisting gasketon the outside is indicated at 5.

What is claimed is:

l. A method of sealing the metallic part of an electrical fitting to aceramic part thereof which comprises, providing a lling of a cementingmaterial mainly of styrene between the metal and ceramic parts of thetting, providing a gasket containing a small amount only of styrene atan exposed surface of the cementing material and then hardening thecementing material and the gasket by polymerization of the styrene insitu to bond to the walls of said electrical fitting parts and to saidgasket.

2. A method according to claim 1 wherein said cernentingmaterialcomprises styrene which has been plastcized by adding thereto anamount not over 25% of a homocyclic carbon compound having not'less thantwo and not more than three fused rings, said compound having a boilingpoint higher than 240 C. and a symmetrical arrangement of polar groups.

3. A method according to claim 1 wherein said cementing materialcomprises styrene blended with rubber.

4. A method according to claim 1 wherein said cementing materialcomprises styrene and an aliphatic olene such as polyethylene, orpolyisobutylene.

5. A method according to claim 1 further comprising, controlling thetemperature of the cementing material during polymerisation to produce aproduct having the required degree of tenacity and resiliency.

6. A method according to claim 1 wherein said cementing materialcomprises styrene that has been polymerised before application to thefitting, plasticized by addition of a controlled amount of monomericstyrene.

7. A method according 'to claim 1 wherein said gasket comprises a rubberand styrene mixture.

8. A method according to claim 1, further comprising providing aweatherproof seal containing a small amount only of styrene, and bondingsaid cementing material to said seal by said polymerisation in situ.

gasket, and a weather resisting seal containing a small amount only ofstyrene and bonded to the cementing material and the fitting partsexternally of said fitting.

THOMAS ROBERTSON SCOTT. LEONARD ARTHUR CHARLES POOLEY.

